1. Field of the Invention
The present invention relates to a control method for a printing apparatus that performs printing by moving a recording head in a direction perpendicular to the direction of conveyance of a copy sheet. More particularly, the present invention relates to a control method for a printing apparatus in a head maintenance operation to restore a recording state of a recording head in the middle of a recording operation.
2. Description of the Related Art
FIG. 3 shows one example of printing apparatus. The printing apparatus shown is a so-called serial printer, which performs printing by moving a recording head in a main scan direction in perpendicular to a direction of paper conveyance (i.e., a sub scan direction). The printing apparatus thus repeats the process of printing in the main scan direction and moving a recording medium in the sub scan direction. FIG. 4 is a sectional view of a major portion of the printing apparatus of FIG. 3. An automatic paper feeder 1 feeds a recording medium to a recording position where the recording head performs printing. Although the automatic paper feeder 1 usually stores a stack of recording media, only one of the recording medium is picked up by a paper feed roller 5 at one time and is supplied to a recording area 8 within a printing apparatus in operation. The recording medium 4, interposed between a pressure roller 6 and a paper conveyance roller 7, advances in an intermittent manner while a recording head (not shown) installed on a carriage 2 performs printing in the course of movement in a main scan direction (namely a direction in perpendicular to the direction of paper conveyance). A diversity of recording heads carry out different printing methods, and an ink-jet recording head, for example, has a portion with a plurality of discharge nozzles mounted therein. In operation, a head maintenance operation to be described later is carried out as necessary. The recording medium 4 that has undergone the printing is then discharged into a discharge tray 3.
The paper conveyance roller 7 rotates when supplied with drive power by a drive motor through a drive gear train (not shown). The pressure roller 6, in contact with the paper conveyance roller 7 or the recording medium 4, also rotates in combination therewith.
In the drive gear train, gears must be meshed with each other with a high degree of precision to accurately transfer the drive power of the drive motor. If the gears abut tightly each other with some load working therebetween, the gears may be damaged due to a mesh degradation and generate mechanical noise. To improve durability and increase low-noise performance, the gear train is typically provided with a backlash.
Specifically, a maintenance unit 9 for carrying out the above maintenance operation may be a suction unit for an ink jet head, a wiping unit for cleaning the face of the ink jet head (where discharge nozzles are arranged), an extra discharging unit for the ink jet head for discharging ink without printing, or some other similar unit. The maintenance unit 9 thus performs the function required to stabilize the printing operation of the ink jet head. Since such a maintenance unit is typically arranged outside the recording area, the maintenance operation is carried out after moving the recording head to the position of the maintenance unit. The maintenance operation typically involves moving the recording head, namely, the carriage 2, out of the recording area. The frequency of maintenance operations changes depending on the pattern to be printed in the printing operation (or a xe2x80x9cprint patternxe2x80x9d) and environmental conditions such as temperature and humidity. To perform a high quality printing, the maintenance operation is performed several times during the printing of a single page.
Referring to FIG. 5, a sequence of the head maintenance process, in the middle of a printing operation, is discussed. The following example is a so-called single direction recording system in which an image is formed when the carriage 2 goes in the main scan and no image formation is carried out when the carriage 2 returns.
In the recording operation, the recording head discharges ink while the carriage 2 scans, and an image is formed on the recording medium 4 (step S501). The paper conveyance roller 7 rotates by a predetermined quantity of rotation to convey the copy sheet while the carriage 2 moves in its back scan direction (in the return direction), and the recording head is prepared to print a next line (step S502).
It is determined in step S503 whether the recording head needs maintaining. When it is determined that a head maintenance operation job is needed, the process goes to step S504 to execute a head maintenance operation. The process returns to step S501 as necessary subsequent to the head maintenance, and steps S501 through S504 are repeated.
When a head maintenance job is performed in the above conventional sequence, the carriage 2 is transferred to a maintenance position prior to the head maintenance operation. The range of scan in the head maintenance operation is different from that in a normal recording operation without performing the head maintenance job. In the head maintenance, the apparatus suffers from a vibration different from the vibration which is generated when the entire apparatus repeatedly scans in the normal printing operation. When a recording operation is executed in immediate succession to the execution of a head maintenance job, a printed image is subject to disturbance. The following causes of the disturbance are contemplated.
The entire apparatus vibrates due to the operation of a drive system that executes the head maintenance. Under such vibration, the paper conveyance roller 7 rotates by a small quantity of rotation corresponding to the backlash of the gear train, causing the recording head to be subject to a relative position error, and thereby leading to a landing error of an ink jet in the direction of paper conveyance. As a result, the printed image is disturbed. When the entire apparatus vibrates due to the operation of the drive system that executes the head maintenance, the vibration is transferred to the recording medium, causing it to vibrate, changing a distance to the recording head (i.e., the distance between the head and the copy sheet), and leading a landing error in the scan direction of the carriage 2 and a disturbance in the printed image.
In view of the above problem, the present invention has been developed. It is an object of the present invention to provide a printing apparatus and a control method for the printing apparatus, which outputs a good quality image by controlling a position error of a recording medium taking place in a head maintenance job in the middle of a printing operation and a vibration of the apparatus.
To resolve the above problem, the present invention provides a control method of a printing apparatus including a conveying unit for conveying a recording medium, a carriage with a recording head mounted thereon, and a maintenance unit for performing a maintenance job on the recording head, wherein the printing apparatus performs recording by intermittently operating the conveying unit to intermittently convey a recording medium by a predetermined travel and by causing the carriage to scan with the conveying unit stopped. When the recording head is maintained by the maintenance unit in the middle of the printing operation, the apparatus controls so that the operation of the conveying unit is stopped subsequent to the finish of a maintenance job.
A printing apparatus of the present invention includes a conveying unit for conveying a recording medium, a carriage with a recording head mounted thereon, and a maintenance unit for performing a maintenance job on the recording head, wherein the printing apparatus performs recording by intermittently operating the conveying unit to intermittently convey a recording medium by a predetermined travel and by causing the carriage to scan with the conveying unit stopped. The printing apparatus includes a control unit for performing control so that the operation of the conveying unit is stopped subsequent to the finish of a maintenance job when the recording head is maintained by the maintenance unit in the printing operation.
In accordance with the present invention, when the maintenance of the recording head becomes necessary in the middle of printing operation to the recording medium, the conveying unit is controlled so that the conveying unit is operated subsequent to the maintenance job. Even if the apparatus suffers from a vibration in the course of the maintenance of the recording head, the entire apparatus is set to a normal printing state, namely, a state as if no maintenance job were done, before the apparatus resumes a printing operation. The image disturbance due to the vibration of the apparatus is thus prevented. Even if the recording medium is in position error due to the vibration subsequent to the maintenance, the error of the recording medium is covered because the conveying unit has operated subsequent to the maintenance.